Engineer and biophysicist Hugh Herr knows what it’s like to lose a limb. He also knows how important it is to have reliable prosthetics that get you back in the game. A double amputee himself, Herr heads the Biomechatronics research group at the Massachusetts Institute of Technology (MIT) Media Lab, as well as his own forward-thinking enterprise, BionX, for researching prosthetic technology to help users reach new heights. ABILITY’s Chet Cooper and Lia Martirosyan recently caught up with the inventor.
Chet Cooper: Before we talk about your projects, can you talk about your experience mountain climbing in New Hampshire?
Hugh Herr: Sure. It was 1982. I set out with my climbing partner Jeff Batzer to climb Huntington’s Ravine up a particular ice climb called Odell’s Gully, which is about an 800-foot ice climb. We climbed up without incident. The weather got increasingly worse, and we made the mistake of going towards the summit from the top of the ice base. The conditions got worse and worse as we marched on, to the point where it was a complete whiteout with blizzard conditions. We were barely able to see. The thing about the summit region of Mount Washington, it can have areas that are flat and rolling. In those conditions, it’s very difficult not to become disoriented, because it’s not like you’re on a face where you know what’s up and what’s down. You’re on a flat surface. Every direction is the same in a white-out condition. And with wind speeds constantly changing direction, within a minute you have no idea where you are.
Cooper: Did you also lose your sense of balance?
Herr: We did later, when we had severe frostbite, and we no longer could feel our lower limbs. We weren’t getting the proprioceptive feedback necessary to balance. So we descended into what’s called the Great Gulf region of Mount Washington, which is the wilderness side of the mountain with the most heinous of bushwhacking. When we hit tree line, we realized that we were off-course, but we could not retrace our tracks because the wind speeds were so high near the summit of the mountain that one could not even stand. So we were forced to go down the Great Gulf.
The average depth of snow was to the waist, sometimes to the chest, so we had tremendous difficulty moving. We probably did a mile a day with about the effort it takes to run a marathon, because of the very deep snow. We went for nearly four days, and we got ourselves to within a few miles of a roadway but couldn’t walk any more. Luckily, a person was out snowshoeing for the day and came across our snow cave and went to get help. We were rescued via helicopter.
Cooper: Did he survive?
Herr: Yes. We both had severe hypothermia, but we survived that. We also both had severe frostbite. As you know, I lost both of my legs below the knee. Jeff lost one leg below the knee and on his other leg he lost half of his foot. On his right hand, he lost a few fingers and fingertips.
Cooper: Has Jeff been able to take advantage of some of the devices that you’ve been working on and inventing?
Herr: Not yet, but I’m confident it’ll happen in the future. In my company, BionX, we have the first power foot-ankle bionic limb in the world. We’ve now fit it to 1,200 people, half of them wounded US soldiers. However, we only have reimbursement for 15 percent of the US population. We have reimbursement for veterans and recently injured soldiers and persons who lose limbs in the workplace and have workman’s compensation. Everyone else, we have great difficulty getting the limb paid for, but we hope in a year or two that will be solved, and then Jeff can certainly try the bionic limb.
We’re also doing research on how a prosthesis attaches to the body mechanically, which is called the socket. We can now mathematically derive an optimal socket for comfort. That technology isn’t out yet, but I hope to make it available to everyone in just a few years.
Cooper: The device then that is available, can you give a brief description of how that works for a person walking?
Herr: Sure. From my MIT lab, so far there have been two products produced commercially. One is a computer-controlled knee and the other is a foot-ankle device. With the foot-ankle device, each unit or foot ankle has three computers and 12 sensors. When it’s powered, the ankle joint is actively actuated and controlled by the three computers. It emulates muscle function that once spanned the ankle joint, providing a person with natural stiffness and powers, enabling them to walk at normal speeds and at normal metabolic rates for the first time in history. That means that if you put a box around a human being and you only get to measure how fast they walk and how much energy they use when they walk, you can’t tell whether the human being has bionic limbs or completely natural limbs. Which is pretty fun. It’s progress.
Cooper: How do you connect it to the leg?
Herr: Most patients in the world have what’s called a socket. It’s a non-invasive mechanical attachment to the residual. It’s basically a custom-made cup that you put the leg into and then if the socket is made properly, you can stand and walk with no pain. It’s that interface that I mentioned earlier. We can now mathematically derive the shape and stiffness of that interface for optimal comfort, which is really, really exciting.
Cooper: So computers are picking up these different sensors?
Herr: Right. And the synthetic sensors measure force, torque, position, speed, acceleration and temperature. All that gets fed into the computers, and the computers have to decide how the motor should be controlled.
Cooper: Why temperature?
Herr: Because if you’re in Phoenix, Arizona, in July and you’re mowing your lawn with a push mower, the motor will just overheat. So it protects itself from high temperatures. If it gets too hot, it’ll start reducing its own power until it cools down.
Cooper: Until the patient or the person using it realizes that they need to take a break?
Herr: It’s nothing wildly dramatic, but they’ll notice a little bit. It’s like a human stopping and taking a cold drink of water to cool down.
Cooper: I also read somewhere that you were dealing with drop foot. Is this technology used to deal with that condition?
Herr: Drop foot is a condition where a person has a biological leg, but the muscles that span the ankle in front of the leg or the anterior muscles are weak or paralyzed such that when they walk and they hit their heel—a heel strike—the forefoot slaps on the ground. We build what’s called an orthosis, which is a fancy word for a brace that’s motorized, where we can add in virtual muscles so the motor can be controlled in a way that the impaired biological limb plus the worn orthosis adds up to a normal dynamical response.
Cooper: So it’s a similar computer process that you’re using for the ankle?
Herr: Somewhat similar, yes. The difference is, in the orthosis, the biological limb is in the loop, in parallel, and in the prosthesis it’s not in the loop. Let’s say the person has some muscle function, but it’s weak. In the prosthetic case, there’s by definition no muscle function, so the motors have to do 100 percent. In orthosis, the motors may only have to do 50 percent because the biological muscle can do the other 50 percent.
Cooper: And when you’re talking about the percentage of the muscle, you’re talking about the muscle to raise the foot, or the lower leg itself that may be having a problem?
Herr: It’s the muscle—if you lift your foot off the ground and move your toes towards the ceilings, it’s those muscles that are weak in the case of drop foot. We have technology to treat weakness anywhere in the ankle. We can also treat the calf muscles, which are what you use when you point your toes.
Cooper: And that’s on the market now, too?
Herr: Not yet. I’m working very hard to get that done. Hopefully, we’ll have something in the market in three to five years. We’re trying to raise money now. It’s not about us not knowing what to do, it’s just about getting the money and hiring the engineers and getting it done.
Cooper: So right now what you have is the idea? There isn’t a prototype built yet?
Herr: Right. If you gave me $7 million, my team could get it launched in about 22 months. We’re trying to find those dollars.
Cooper: The devices you’re now using yourself, are they a combination of products that you’ve developed for your own use?
Herr: Very good question. Before about 2009, no part of my prosthesis did I design, simply because I never focused on my own needs in my inventing. I invented shoes and knees and crutches and all these things that I don’t use. But we did this foot-ankle, and now I’m wearing it full-time. The part of my limb that I’m still using that my team didn’t design is the socket interface that I mentioned. But that will change in about one month. In a month, every part of my limb will be something that my team developed, which is a lot of fun. It’s really cool. Again, we’re using mathematics to design the most comfortable fit, and then we’re going to be 3D printing the interface out of titanium and polymers. We can make it really, really beautiful as well. It’ll be fun.
Cooper: So part of the customization that you’re seeing with the other products connects with 3D printing?
Herr: The vision is that in the future, every human will have a digital model of their body stored in computers. When someone needs a new shoe or a new bra or a new prosthesis or a new brace, s/he’ll just fabricate it from the digital model themselves and then the device or article will be delivered to the home without even having to go to a retail store. The shoe, the bra, the brace, it’ll be the person’s apparel, the person’s device, no one else’s. It’ll be exquisitely comfortable and functional. So this whole notion today where we have sizing to fit across humans is just utterly absurd. We’re really asking, what does it scientifically mean when something’s comfortable versus when something’s not comfortable? What are the properties of something comfortable versus not comfortable?
If we can answer that, we can produce optimality using mathematics, really fast computers and digital models of humans. What is the optimal bra for a particular woman? Those are the questions we’re asking. Just in persons with limb amputation alone, which is approaching 20 million people, all 20 million people are uncomfortable, sometimes in a lot of pain, with today’s prostheses.
Cooper: What I’m picturing now is that those people who do the fitting, they will become maybe outlets to do the imagery for the individuals to store the data you’re talking about?
Herr: Now we’re using these multimillion-dollar imaging devices to collect the data to build the mathematical descriptions of the human body. But what I want to do is invent new devices where you can collect that data with small, inexpensive technology. And then I want to ultimately have those tools distributed globally, where everyone has access to them.
Cooper: So maybe partnering with another company to develop that capability?
Herr: [pause] Maybe, but it will probably be a new company. We’re developing the technology right now.
It’ll be about two years from now or so. In that future world, when a person needs a new artificial limb, let’s say the left leg is amputated, not the right leg; the person can digitally map the residual limb, the left leg, and s/he can also digitally map the right leg that’s intact, and all that data will go to a central fabrication facility with really fast computers. The whole limb will be designed, and if the person wants, it’ll be perfectly symmetric with their biological leg and optimally comfortable. And the limb will be shipped in the mail. They’ll be no need to visit a clinician to get the thing made. That’s an outlandish vision that will take a while to develop, but that’s where the world is going.
Cooper: And it’ll be delivered by a drone?
Herr: [laughs] That’s right!
Cooper: Will people go somewhere to do the mapping?
Herr: No. In the most audacious vision, the users have the mapping tools, and they map their own bodies.
Cooper: So it’s a one-off. Maybe it’d be something like a shared device that could be moved around. I just heard something on NPR this morning about the peerto-peer expansion in Europe with cars, where you rent somebody else’s car and drive it.
Herr: Maybe the device will be so affordable that a person can just own it. In the worst case, the person will have to go to a community center or something to get themselves mapped.
Cooper: Maps ‘R Us. How big is your team? You’ve got a lot of projects you’re working on.
Herr: It’s remarkably small. My MIT group is about 35 people, and my company is about 55 people.
Cooper: That’s a lot of people for your company. Right now you have your limitations because of financial reasons?
Herr: Yeah. We’re not short of ideas. Finances completely determine what we can do and how quickly we can move.
Cooper: On a daily basis, do you go into the lab? What are most days like for you?
Herr: My busiest day in the lab is when I meet with every single student, and we talk about their project, their progress, and how to overcome difficulties. I try to do that on a weekly basis. It’s hard guiding the ship and doing what I need to do to raise money.
Cooper: And on your free days, do you still do any climbing?
Herr: I’ve been trying to go to the gym just in my daily life here. The last time I climbed outside was in August. I went to the Italian Alps, to the Dolomiti, and did some climbing just north of Venice. I may be going to Jordan in April.
Cooper: Is there something to climb in Jordan?
Herr: Oh, yeah, it’s remarkable.
Cooper: I guess there has to be something, because the Dead Sea is right there, and that’s the lowest place on the planet.
Herr: They have very, very high cliffs.
Cooper: Now that I think about it, I remember driving up from the Dead Sea on the Jordanian side and driving up, up, up.
Lia Martirosyan: Have you been to Armenia and climbed there?
Herr: I haven’t. I’ve been to Israel. I’ve been to Serbia, but I didn’t climb there. In Europe, I’ve mostly climbed in Italy. The Dolomites are my favorite mountain range in the world, so far.
Cooper: When you were in Israel, did you talk to any other scientists, like the people who are working on the robotic exoskeleton?
Herr: I did visit ReWalk years ago.
Cooper: We were just there a few months ago. I can’t remember the doctor’s name that heads up the project.
Herr: They’ve made a lot of progress.
Cooper: But it’s heavy, the battery-powered equipment.
Herr: I know.
Cooper: They wouldn’t even let Lia try it on. It just didn’t fit with her. She’s petite, and they wouldn’t even allow her to try a demo to see what it’s like; they were too concerned because of the weight of the apparatus. Tell me the most exciting thing that’s happened recently in your work that you didn’t expect to accomplish.
Herr: It’s obvious. I’m excited about this new fitting technology, and our various neural projects are very exciting, trying to get information in and out of nerves. It has a lot of potential. We haven’t translated yet to humans. I look forward to that.
We have a whole program on neural control. We’re trying to communicate from the peripheral nervous system, from nerves and muscles, to an external limb, and then also take sensory information from the external limb and stimulate into the nervous system.
Cooper: How do you test for that? Do you work with animals?
Herr: Sometimes. As quickly as we’re able, we try innovations on human users. That’s the dominant point. Humans are able to give very good feedback. You can’t tell with an animal what they feel.
Cooper: Or say, “Lift your back left leg, please.” When you get to that point, do you need a physician to be working with you to connect the muscles?
Herr: As part of the Center for Extreme Bionics at MIT, I’ve brought in and teamed with world-class plastic surgeons. We’re redefining the surgical procedure as to how limbs are amputated. It fundamentally hasn’t changed for a very long time, since the Civil War. We’re redefining what’s done with the nerves and muscles and bones when a limb is amputated, to make it more conducive to a neural interface and a mechanical interface. So yes, surgical technique is very much part of the research.
Cooper: I never thought of it that way—that there has been such slow progression. I do know that when someone is in the right center somewhere in the world for amputation, doctors start to think about the prosthetic. Oftentimes, they’re more involved in just saving a life than what’s happening after the fact.
Herr: Also, amputation amongst many surgeons is considered a failure. It’s like, “Oh, we didn’t solve the natural limb. OK, cut it off.” I want to change that so BionX is part of the menu of options for the clinician who rebuilds limbs, where they’re not tissue-centric and simply ask the question, “What’s the best thing to do for the patient to improve the quality of life?” That may be trying to repair tendons and ligaments or it may be amputating the limb and getting the person bionics. They put the poor human patient through multiple
surgeries and years and years and years of agony and a sedentary lifestyle, and often the patient turns on the TV and they see me climbing or some other person sprinting or doing something incredible, and they ask the very natural question, “Why the hell am I lying in bed all the time with a limb that doesn’t work?” And then they beg their medical team to just amputate the limb, and they finally succeed at convincing their doctors to do that, and they’re up and going within six months. They’re like, “I wasted years trying to quote-unquote save the biological limb.”
Limb reconstructionists are thinking in that way, but many are still what I would call old-fashioned in their views. Somehow, even if the biological has some pathology and is non-functional in some way, it’s always better than a synthetic one. In many cases now, it’s simply not true, but we still have a bias towards the biological limb.
Cooper: We did an article about someone—he’s now a model, I guess—who had that mindset to say, “This is just not working. Can you take the leg off?” It changed his life completely for the better.
Herr: Viktoria Modesta was born with a birth defect and had a limb that didn’t work throughout her whole childhood. She finally convinced her doctors to amputate the limb, and now she’s this crazy, rising pop star in the world. Google her name and check out her most recent music video. It’s fantastic.
Cooper: You’re saying that with the procedure, her voice got better?
Herr: (laughs) Maybe. But seriously, she went from a young lady in high school and middle school, being very unpopular and made fun of, to an international star with a pronounced physicality in just a few years. It’s a very interesting story.
Cooper: What do you think about people racing with one-leg amputee versus dual-leg amputee? Is that an even race?
Herr: Oh, boy. [pause] My colleagues and I studied the biomechanics and physiology of running with those prostheses for about three years. Our conclusion was, we did not see any overall advantage to using such prosthesis for a sprinting performance.
Cooper: You didn’t see a difference?
Herr: Oscar Pistorius and others who have used and are using the prosthesis, our results are that their physiology is the same. They use the same amount of energy, they fatigue at the same rate, but the mechanics of how they run is different than a person with biological limbs. In a biological human, when a human sprints, it changes its stiffness dramatically when the foot is in contact with the ground. A lot of that stiffness variation comes from the ankle. So if you replace the biological ankle with a dumb spring, you can’t get that stiffness modulation that results in very, very high forces being generated on the ground, which is important for running fast.
So to exaggerate, a person who is running on these passive springs, it’s like running on a soft mattress compared to a more rigid surface. That’s an exaggeration. It’s not that bad. But to kind of get your head around it, that’s what it’s like. Comparing two athletes with the same athleticism, we believe that a person with both legs amputated cannot generate as high forces on the ground as a person with biological limbs. So how people make it up is, they swing their limbs fast in the aerial phase of running. They get the leg ahead of them quickly. And perhaps they exploit the fact that the spring leg is lighter than the biological leg to do so. So there’s kind of a disability when their foot’s in contact with the ground, because they can’t generate these high forces, and then they kind of make up for it by swinging their legs back and forth faster. That’s kind of the hypothesis that we ended with.
If you watch films of Oscar Pistorius running, listen to his running. You’ll notice that the frequency of foot strikes is very, very high. But he’s running soft, like he’s running on a mattress. And what’s remarkable is that the energy he uses is the same as if he had biological limbs, and his rate of fatigue is the same. Physiologically, we could never see any difference. So there’s these inane arguments that if you cut someone’s legs off and put springs on them, then obviously they use less energy because they don’t have to fuel the muscles, which is the most idiotic argument, especially for a Pistorius, because he got artificial limbs when he was one or two years old, and throughout his childhood he was running and trying to keep up with his brothers, so his entire physiology is adapted to the running ones. So his muscle mass around his hips is huge, because that’s where his engine is, because he doesn’t have natural ankles. His engine is his hip. That world of thinking that you cut off limbs and someone can run with less energy is naïve, because it doesn’t comprehend that the physiology completely re-adapts because the limbs are amputated and you put two passive springs beneath the limbs.
Cooper: Interesting. Great question I had there! I didn’t know you did that research.
Herr: Oh, yeah. Pistorius was banned from the Beijing Olympics. There was a law firm in New York City that took on his case pro bono. That law firm called me and asked if I would be an expert witness pro bono.
Cooper: And who would have known all that other stuff would have happened?
Herr: So for years we studied the problem. If you go to my web page at MIT, you can see lots of papers on the topic. And my colleague, Alena, at the University of Colorado at Boulder is still studying the problem.